Probiotics, foods containing live 'friendly' bacteria that some evidence suggests helps in digestion, have a tangible effect on the metabolism, according to the results of a new study in the journal Molecular Systems Biology.

The research is the first to look in detail at how probiotics change the biochemistry of bugs known as gut microbes, which live in the gut and which play an important part in a person’s metabolic makeup. Different people have different types of gut microbes inside them and abnormalities in some types have recently been linked to diseases such as diabetes and obesity.

For the study, researchers from Imperial College London and Nestlé Research Center, Lausanne, Switzerland, gave two different types of probiotic drink to mice that had been transplanted with human gut microbes.

The researchers compared the levels of different metabolites in the liver, blood, urine, and feces of mice who had received treatment with probiotics and those that had not.

They found that treatment with probiotics had a whole range of biochemical effects and that these effects differed markedly between the two probiotic strains, Lactobacillus paracasei and Lactobacillus rhamnosus. Adding ‘friendly’ bacteria changed the makeup of the bugs in the gut, not only because this increased the number of such bacteria, but also because the ‘friendly’ bacteria worked with other bacteria in the gut, amplifying their effects.

One of the many biochemical changes observed by the researchers was a change in how mice treated with probiotics metabolized bile acids. These acids are made by the liver and their primary function is to emulsify fats in the upper gut. If probiotics can influence the way in which bile acids are metabolized, this means they could change how much fat the body is able to absorb.

Professor Jeremy Nicholson, corresponding author on the study from the Department of Biomolecular Medicine at Imperial College, explained “Some argue that probiotics can’t change your gut microflora - whilst there are at least a billion bacteria in a pot of yoghurt, there are a hundred trillion in the gut, so you’re just whistling in the wind.

“Our study shows that probiotics can have an effect and they interact with the local ecology and talk to other bacteria. We’re still trying to understand what the changes they bring about might mean, in terms of overall health, but we have established that introducing ’friendly’ bacteria can change the dynamics of the whole population of microbes in the gut,” he said.

The researchers hope their new insights about how probiotics and gut microbes interact will ultimately enable the development of new probiotic therapies, which can be tailored for people with different conditions and different metabolic makeups.

Dr. Sunil Kochhar, another author on the study from the Nestlé Research Center, added: “Understanding changes in the molecular events triggered by the so-called beneficial bacteria in the host metabolism is an important prerequisite in our efforts to develop customized nutritional solutions to maintain and/or enhance our consumer’s health and wellness at an individual level. The results of this study are highly promising to address personalized nutrition.”